Vacuum tube



July 19, 1960 w. s. GEISLER, JR 2,945,980-

VACUUM TUBE Filed July 2, 1954 ob 8 I i in Mm.

& ||||H Wilson .5. Gal's/er, Jr.

Q S. 812g,

Patent Agent 2,9453% VACUUM runs Wilson S. Geisler, J12, Atherton,Calif., assignor, by mesne assignments, to Applied RadiationCorporation, Walnut Creek, Qalifi, a corporation of California FiledJuly 2, 1954, Ser. No. 441,087

3 Claims. (Cl. 315-3.5)

To enable the production of tubes which are, relatively speaking, clean,that is, are evacuated to a high degree, it has been conventionalpractice to raise the tubes to a relatively high temperature -during theevacuation cycle. However, certain inherent limitations in just how highthe temperature may be raised are encountered because of the physicalelements which make up the tubes. In most tubes of the type with whichthe present interest lies, this limitation is set by the glass elements,glass having a softening temperature of approximately 475 degreescentigrade. As a consequence, tubes which contain glass elements arenormally baked out and evacuated at 450 degrees centigrade or less. Thismeans an incomplete vacuum is obtained and the particles which remainwithin the vacuum envelope of the tube become ionized upon subsequentoperation thereof to cause maloperation of the tube and hastening ofcomplete tube failure. For example, it is known that failure-of acathode is most frequently the result of positive ion bombardment. Asanother example, the noise produced in microwave tubes is a directresult of the ions therein. While the production of noise is indeedserious in klystrons, it is yet more accentuated in other microwavetubes such as traveling wave tubes wherein the electron beam must ofnecessity traverse a path of considerably greater length.

Consequently, it is an object of the present invention to providemicrowave tubes which are constructed of parts so that higher bakeouttemperatures than those presently utilized may be applied to enable theproduction of more highly evacuated devices. A feature of the inventioninvolves the provision of a tube constructed of ceramic and metalelements which will withstand high bakeout temperatures.

A further feature involves the provision of an electron 'gun structurefor microwave tubes of a novel ceramic and metal construction.

Yet another feature involves the provision of an improved vacuum tubeconstruction which is inexpensive, particularly easy to assemble and,generally speaking, readily applicable to quantity production. 7 Otherfeatures, as well as the advantages of the present invention, willbecome more apparent from a perusal of the following description of theaccompanying drawing wherein: Y Figure l is a central, longitudinal,sectional View of a traveling wave tube embodying the present invention,

' Figure 2 is an exploded view of the elements which make up theelectron gun in Figure 1,

Figure 3 is a central sectional view of a reflex klystron embodying thepresent invention, and

Figure 4 is an end View of the reflex klystron.

As shown in Figure l, the traveling wave tube generally includes anelectron gun adapted to produce a beam of electrons that traverse a paththrough a slow wave structure 11 to thereafter be collected upon acollector electrode 12 disposed at the far end of the tube. Asconventionally utilized, the electrons during their traversal portion ofthe tube shown nited States Patent ice through the slow wave structure11 are so directed by suitable focusing coils (not shown). as tointeract with a radio frequency wave that is applied to such structurein any of a number of known manners, but preferably by means of radiofrequency couplers such as disclosed in my co-pending application,Serial Number 429,265, filed May 12, 1954. v

In order that the desired interaction be had, the electron gun 10, theslow wave structure 11 and the collector electrode 12 are supported by agenerally tubular vacuum envelope in axial alignment. In accordance withthe present invention, the tube is constructed so that all of its partswhich are within the vacuum envelope, as well as those which define suchenvelope, are composed of materials which will withstand a temperatureof at least 600 degrees centigrade without deterioration of any sort.More particularly, the parts of the tube include conducting members of ametal which'will not melt or be in any way adversely affected byexposure to such a temperature and insulating members, preferably ofceramic, which, unlike glass, will not soften and will not otherwisedeteriorate under this elevated temperature.

The electron gun 10 is arranged in accordance with the present inventionto provide for rigid and accurate support of its internal elements andease of external electrical connection to these elements, while at thesame time, maintaining the utmost simplicity so that the gun may bereadily constructed with an assembly-line type of production technique.For this purpose, the wall of the electron gun defining its vacuumenvelope, is of stacked construction; that is, a plurality of conductingmembers 14,15, 16, 17, 18 that are adapted to support the cathode andother internal elements of the gun are disposed in spaced relation by aseries of insulating mem bers 20, 21, 22, 23. As best shown in Figure 2,the insulating members 20, 21, 22, 23 constitute tubular, ceramic stubshaving like cross sectionbut differing in length. Each of theelement-supporting members 14, 15, 16, 17, 18 constitutes a stamping asof copper or Monel that is generally of angular configuration, beingstepped, as indicated for example at 15, adjacent its peripheral edge sothat it may be interposed and sealed between two of the tubular, ceramicstubs in vacuum tight relation so that the vacuum envelope of theelectron gun 10 is thus defined. The term stamping, as herein used,includes parts which have been subjected to stamping, drawing, cuttingand/or other die-formed operations. The radial portion of the step 15lies between adjacent ceramic stubs with the longitudinal portionstelescoping over and within the two adjacent stubs respectively so as tobe fixed both radially and axially of the electron gun. More centrally,

' the supporting members 14, 15, 16, 17, 18 have a configurationdetermined in accordance with the element of the electron gun 10 thatthey are adapted to support. One of these members 14 which forms thebase of the electron gun is of generally dished configuration having .acentral opening through which a post 24 extends, forming one terminal ofa helical heater element 25. The other terminal of the heater 25 istied, as by spot-welding, to the second of the series of annularsupporting members 15. The heater 25 is supported substantially axiallyof the electron gun 10 and is concentrically surrounded by a thermalshield 26 which is mounted'on the third of the annular supportingmembers 16 and supports at its extremity a cathode button 27 having asuitable coating of electron emitting material upon its surface. Afourth annular supporting member 17 mounts at its central portion afocusing ring 23 disposed in pre-determined annular relation adjacentthe cathode button 27 and a fifth supporting memberlS includes anintegral annular metal disc 29 whose central opening 30 is axiallyaligned with the cathode and is adapted to be supplied with a positivepotential so as to constitute an anode for accelerating the electronsemitted from the described cathode button 27. A suitable getter 31 canbe secured between the second and third of the annular supportingmembers and 16.

The manner of assembly of the described gun will be, from the foregoingstructural description, readily apparent. Briefly, it can involve theapplication of a molybdenum-manganese coating to the ends of each of theceramic insulators 2-3, 21, 22, which are then brought into engagementwith the respective ones of the element-supporting members 14. l5, lo,17, 18, the elements themselves having previously been secured thereon.The ceramic insulators are then secured in vacuum.- sealing relationwith the interposed supporting members by means of a braze, preferablyof copper-gold, and an additional brazc is made to seal the heater post24 within the central opening in the disc-shaped base member 14 to thuscomplete the assembly of the electron gun it).

In order to secure the electron gun id to the remainder of the travelingwave tube, a metallic support 32 of generally cylindrical form issecured, as by brazing, to the described anode 29. At its far end, thesupport 32 is rebent to form an opening adapted to closely encompass theend of a ceramic tube 33 within which the mentioned slow wave structure11 is supported, and when so disposed, the support 32 is sealed to theceramic tube 33 in vacuum-tight relation.

As shown in Figure l, the slow wave structure 11 constitutes a metalhelix, one end of which is spot-welded to a thin-walled metal cylinder34 which is flanged at one end to provide a. lip 35 adapted to restagainst the end of the ceramic tube The helix at its other end isspot-welded to a hook 36 adapted to engage the other end of the ceramictube 33 and to be secured thereat by means of a small tribulation 37which is spot-welded to the hook and is brazed in sealing relationshipwith the end of the ceramic tube 33. As shown in Figure 1, thistubulation 37 at the end of the traveling wave tube is pinched off tocomplete the vacuum envelope of the tube and functions during operationas the previously mentioned collector electrode 112.

Before the described tubulat-ion 37 is pinched oif, it functions as theexit during evacuation of the tube. Because of the all metal and ceramicconstruction of the tube, this evacuation can be carried out while thetube is maintained at a bakeout temperature of 600 degrees centigrade ormore. As previously mentioned, evacuation at this elevated temperatureproduces a cleaner tube which will operate more effectively with, forexample, a lessened noise level, and will operate furthermore in thismanner for considerably greater periods of time. When the completed tubeis supplied with the proper voltages and radio frequency coupling, asare well-known in'the art, areduction in the noise level of 25 percentor more and tube life of great length can be expected.

As will be apparent from the foregoing, the described construction of atraveling wave tube through utilization of a series of stackedconducting and insulating members can be employed with equal aptness tothe fabrication of klystron type tubes. As shown in Figure 3, a reflexklystron embodying the present invention essentially consists of anelectron gun 40 and a reflector section 41 disposed on opposite sides ofa resonator cavity 42. More particularly, the electron gun is arrangedin a manner similar to that previously described with respect to thetraveling wave tube. A heater 43 is connected between a first annularconducting member 44 forming the end of the gun and having an exhausttubulation 45 therein, and a second annular conducting member 46 held inspaced relation with respect to the end by an annular insulating member47, preferably of ceramic material. This second annular conductingmember 46 also supports a tubular heat shield 48 which surrounds theheater 43 and mounts the dished cathode button 49 at one end thereof.Thus, it will be seen that this second annular conducting member 46provides a common heater-cathode terminal. in addition, it provides oneterminal for a suitable getter 50, the other terminal of which consistsof a third annular conducting member 51 supported in spaced relationfrom the second conducting member 46 by a second ceramic insulator 52,such third conducting member being so formed as to mount a focusing ring53 adapted to encompass the cathode button 49. The lengths of theceramic insulators are individually such that suii'icient insulation isprovided between the various tube elements to preclude voltage breakdownat the applied D.C. potentials.

An accelerating grid 54 is held in spaced relation to the cathode button43, being curved so as to conform to the dished configuration of itssurface. The accelerating grid 54 is supported in this position on ametal cup 55 held in insulated relation with respect to the electron gun46 by an additional ceramic insulator 56 and having a drift tube 57formed integrally therewith centrally in its base portion so as to beaxially aligned with the cathode button 49 and the accelerating grid 54.This drift tube 57 enters and is secured within a central apertureformed in the base of another metal cup 58, Whose internal dimensionsare such as to determine the resonant frequency of the tube inconjunction with an annular plate 59 which is inserted and brazedtherein so as to form the resonator cavity Suitable grids 60, 61 aresecured at the end of the drift tube 57 and in the central opening inthe annular plate 55 to provide the capacitive gap for the cavity 42.The reflector section 41 includes a reflector 62 supported in spacedrelationship with respect to the capacitive gap on the end of a post 63which is brazed centrally within an annular conducting member 64- formedsimilarly to those utilized in the fabrication of the electron gunportion of the tube and held in insulated relation from the resonatorcavity 42 by an annular ceramic insulator 65 secured at the end of ametallic cup 66 brazed to the extremity of the cavity-forming cup 58,previously described.

Upon application of suitable D.C. potentials from sources (not shown) tothe respective conducting members, electrons emitted from the cathode 49will be accelerated by the described accelerating grid 54 to passthrough the grids 69, 61 forming the capacitive gap and thereafter toapproach the reflector 62 and be repelled for a return crossing of thegap, when in bunched relation, so as to excite oscillations within theresonator cavity 42. To provide for egress of energy from the cavity, asmall opening or iris 67 is formed in one side of the cavity-forming cup58 and is sealingly encompassed by a wave guide stub 63 which is securedin position by brazing to a relatively heavy ring 69 which closelyencircles a major portion of the cavity-forming cup 58. Atthe end of theWave guide stub 58, a ceramic window 70 is suitably secured within aconventional wave guide flange 71.

To enable tuning of the tube, the base of the cavityforming cup 58 isrelatively thin so as to constitute, in effect, a tuning diaphragm whichwhen flexed, varies both the cavity volume and the spacing of the grids60, 61 that form the cavity gap. To enable variation of the diaphragmposition, like flanges 72, 73 are brazed no the exterior of each of thecups 55, 66 which respectively mount the electron gun 40 and thereflector section 41 in the proper disposition relative to the resonatorcavity 42. Three tuning screws 74 are adapted to adjustably join theseflanges '72, 73 so that upon turning of the screws, the whole of theelectron gun portion 40 of the tube will be shifted relative to theresonator cavity 42 so as to cause the previously described change inthe cavity volume and gap spacing. Suitable lock nuts 75 on the tuningscrews 74 enable a desired frequency to be accurately maintained. Sincethis reflex klystron, like the previously described traveling wave tube,is of metal and ceramic construction, it can be baked out in theneighborhood of 600 degrees during evacuation through the describedtabulation 45 at the end of the electron gun so as to produce a highlyevacuated or clean tube, so as to have long life and a lower noise levelthan glass tubes.

Various modifications and alterations of the disclosed embodiment may bemade without departing from the spirit of the invention. For example, itwill be obvious that the described electron gun may be used inconjunction with traveling Wave tubes or backward wave oscillators,having a slow wave structure in the form of a loaded line, rather than ahelix. As a consequence, the foregoing description of one embodiment ofthe invention is to be considered as exemplary and not in a limitingsense and reference is made to the appended claims for indication of theactual scope of the invention.

What is claimed is:

1. In a vacuum tube, an electron gun comprising a plurality of elementsadapted to act in concert to produce a pencil-like beam of electrons,said elements being radially displaced relative to the axis of saidelectron beam, and separate means for supporting each of said elementsin spaced, insulated relation including a plurality of insulatingmembers, and a plurality of conducting members one for each of saidelements arranged in alternate stacked relation with said insulatingmembers.

2. In a vacuum tube, an electron gun comprising a plurality of elementsadapted to act in concert to produce a pencil-like beam of electrons,said elements being radially displaced relative to the axis of saidelectron beam, a plurality of annular conducting members each supportingone of said elements, and a plurality of tubular insulating members ofidentical cross-section interposed between said conducting members andarranged to sealingly engage and support the same in spaced relation,said conducting and insulating members forming a portion of the vacuumenvelope of the vacuum tube, said conducting members having likeexterior dimensions but unlike interior dimensions wherefore saidelements are supported in radially displaced positions.

3. A traveling wave tube comprising an evacuated envelope, an electrongun having a plurality of elements, a slow wave structure adapted to beaxially traversed by a beam of electrons from said gun, a collectorelectrode adapted to collect theelectrons after such traversal, andmeans including a plurality of tubular ceramic insulating members andconducting members arranged in alternate stacked relation for supportingthe elements of said gun, said slow wave structure, and said collectorelectrode in spaced relation, and forming said evacuated envelope ofsaid tube.

References Cited in the file of this patent UNITED STATES PATENTS2,464,349 Samuel Mar. 15, 1949 2,521,426 Trump et a1. Sept. 5, 19502,608,664 Van de Graafi et al Aug. 26, 1952 2,619,611 Norton et a1. Nov.25, 1952 2,629,066 Eitel et a1. Feb. 17, 1953 2,640,948 Burn'll June 2,1953 2,680,814 Robinson June 8, 1954 2,684,452 Sorg July 20, 19542,684,453 Hansell July 20, 1954 2,692,351 Morton Oct. 19, 1954 2,828,434Klein et al. Mar. 25, 1958

